Preparation of sodium polymaleate

ABSTRACT

THE SODIUM SALT OF POLY(MALEIC ACID), USEFUL AS A DETERGENT BUILDER, IS PREPARED BY HYDROLYZING POLY(MALEIC ANHYDRIDE) WITH WATER AT 60 TO 80*C., AND SIMULTANEOUSLY ADDING THE AQUEOUS SOLUTION AND A SOURCE OF SODIUM OXIDE INTO A HEEL OF WATER AT PH 9.2 TO 10.6, MAITAINING THIS PH THROUGHOUT THE ADDITION THEN BLEACHING THE SLURRY, AND RECOVERING THE SALT.

United States Patent Office 3,637,609 PREPARATION OF SODIUM POLYMALEATE John H. Blumbergs, Highland Park, Joseph H. Finley, Metuchen, and John J. Rizzo, Trenton, N.J., assignors to FMC Corporation, New York, N.Y. No Drawing. Filed June 1, 1970, Ser. No. 42,542 Int. Cl. C08f 27/04 U.S. Cl. 26078.4 R Claims ABSTRACT OF THE DISCLOSURE The sodium salt of poly(maleic acid), useful as a detergent builder, is prepared by hydrolyzing poly(maleic anhydride) with water at 60 to 80 C., and simultaneously adding the aqueous solution and a source of sodium oxide into a heel of water at pH 9.2 to 10.6, maintaining this pH throughout the addition, then bleaching the slurry, and recovering the salt.

BACKGROUND OF THE INVENTION The commonly used detergent compositions include soaps and synthetic detergents, mixed with compounds known as builders, which act both to improve the detergent power of the primary detergents, and to reduce the cost of the over-all compositions. The inorganic polyphosphates, such as sodium and potassium tripolyphosphate, have been almost universally used as the bulk of the builder constituents in such compositions. However, there has beena growing resistance to the use of polyphosphates, on the ground that they induce the build-up of undesirable vegetation in waters into which the detergents wastes are eventually discharged, and there 'has been a growing demand for detergent builders which would not cause this difficulty. Any such detergent builder must, of course, have optimum economics, and should not produce different environmental hazards than do the phosphates.

Many such builders have been suggested, but all have substantial disadvantages. Nitrilotriacetic acid, which is currently being used commercially as a substitute for phosphates, is both more expensive and potentially dangerous, in that it can keep quantities of heavy metals in solution in water. Other available builders are either much more costly, or have other serious drawbacks.

A potentially interesting group of possible detergent builders comprises the alkali metal salts of poly(carboxylic acid)s as described in Diehl U.S. Pat. 3,308,067, issued Mar. 7, 1967. This patent describes the use, as builders, of the Water-soluble salts of poly(c-arboxylic acid)s, the simplest and least expensive of which are the sodium salts of various poly(maleic acid)s. The salts of poly(maleic acid) are made by homopolymerizing maleic anhydride, hydrolyzing the poly(maleic anhydride) to poly(maleic acid) in an aqueous medium and neutralizing the acid to form the salt, as described, for example, in Berry U.S. Pat. 3,359,246 of Dec. 19', 1967.

The neutralization is apparently a simple step, but difficulties are encountered in attempting to prepare a white sodium polymaleate which is acceptable for use in household detergents. -If alkali is added to water solutions of the acid, as described in U.S. Pat. 3,359,246, there is a marked tendency for salt to precipitate in lumps which occlude acid, unless the salt is kept in solution during the addition of alkali by using sufficient water. Since the solubility of sodium polymaleate is of the order of under 1%, the cost of recovery of salt makes such a dilution uneconomic. If the reverse procedure is used, adding the poly(maleic acid) solution to the alkali solution, the salt precipitates nicely as fine yellow particles; but the produc- 3,637,609 Patented Jan. 25, 1972 tion of white material therefrom with bleach is extremely diflicult and expensive.

OBJECT OF THIS INVENTION STATEMENT OF THE INVENTION We have found that the object can be attained by (1) preparing an aqueous solution of poly(maleic acid) at a temperature not in excess of about C.; (2) preparing an aqueous solution of a source of sodium oxide to react with the acid; (3) feeding the two solutions into a heel of water at pH about 9.2 to 10.6 and maintaining the reaction mixture within that pH range and at a temperature not above about 80 C. throughout the addition, to obtain a slurry of salt in a solution thereof; (4) bleaching the slurry while maintaining the pH range; and (5 recovering bleached salt from the reaction mixture.

DETAILED DESCRIPTION OF THE INVENTION Poly (maleic anhydride), the basic raw material for the process of this invention, is prepared in known manner, as described in Berry U.S. Pat. 3,359,246, or more preferably by the methods described in the Blumbergs et a1. applications S.N. 758,678, filed Sept. 10, 1968-and S.N. 862,059, filed Sept. 29,1969. The poly(maleic anhydride)s produced will have an average of from at least 3 units per molecule to about 500, with typical molecular weights of the order of about 5,500 to 25,000.

The first step in the process involves hydrolysis of the poly(maleic anhydride) to poly(maleic acid). This can be done by using water at temperatures near the boiling point for a short period of time, for example 30 minutes at C., as described in U.S. Pat. 3,359,246. We prefer to operate at about 60 to 80 C. for 1 to 2 hours, in order to reduce decarboxylation which we have found occurs at temperatures near the boiling point. Maleic anhydride can be kept at C. for an hour in a 21% aqueous solution with a loss of only 0.02 mol percent of CO In contrast, a typical poly(maleic acid) will lose 1.6 mol percent under the same conditions, and a partially neutralized poly(maleic acid) (pH 4.75) will lose 4.3 mol percent of CO At 50 C., the losses are one-third of what they are at 100 C.

The solutions of poly(maleic acid) prepared should be sufliciently concentrated to permit economic operation. We prefer to operate as close to the solubility limit of the acid at the temperatures of operation as is technically feasible. Since solubility increases with temperature, we prefer to operate close to 80 C., this upper limit being selected, as indicated above, to minimize decarboxylation of the product. In this temperature range, about 20% solutions of the acid represent a convenient concentration. We can, of course, operate at much lower concentrations, of the order of a few percent, since the salt has a solubility of under 1% in water; but operations at lower concentrations are, of course, more expensive. Operations at temperatures below 60 C. are feasible, and we have operated to below ambient temperatures; but since the solubility of the poly(maleic acid) drops, we prefer to operate between 60 and 80 C.

The rather concentrated acid solution is then run into a heel of water at pH about 9.2 to 10.6, at the selected temperature; the pH is maintained through the reaction, and the temperature is kept below 80 C. Simultaneously, an aqueous alkali is added, to maintain the pH within the above limits. The amounts of water in the heel and in the alkali are kept minimal for cost reasons; we prefer that the final concentration of salt is at least 10%. At this concentration and at these temperatures, almost all of the salt precipitates, to form an aqueous slurry, in the form of finely divided pale yellow particles. We have used sodium hydroxide, sodium carbonate and sodium sesquicarbonate as sodium oxide sources in our work.

The slurry is then treated with a bleach, such as hydrogen peroxide, peracetic acid, sodium hypochlorite, perbenzoic acid or ozone, and bleached to a whiteness of at least 90% as measured by photoelectric tristimulus colorimetry with a magnesium oxide standard, with a Zeiss Elrepho colorimeter. The bleach is conducted within the same pH limits as the precipitation, i.e. 9.2 to 10.6. Since the solid salt does not decarboxylate readily, any convenient bleaching temperature may be used.

Finally, the slurry is evaporated to dryness to obtain the desired end product. The slurry may be evaporated to dryness at room temperature, or under vacuum, or it can be spray dried if desired.

It should be noted that the sequence of reaction is most important. If the alkali solution is added to the acid solution, gummy, sticky lumps begin to precipitate when the pH reaches about 7.0, when about half the alkali has been added, If the acid is added to the alkali, a fine yellowish precipitate is obtained, which is very difiicult to bleach. Direct comparison on a number of trials gave creamy products with a whiteness of the order of 75 to 85, as against 92 to 95 for products produced from the identical raw materials, concentrations and temperatures using the simultaneous controlled addition technique of this invention.

Moreover, the salt must be bleached and not the poly- (maleic acid). Using a variety of bleaches (70% hydrogen peroxide, sodium hypochlorite with 5.5% of available chlorine, 40% assay peracetic acid, 33% assay perbenzoic acid in tertbutanol, and ozone) on the acid, salts were obtained with the very poor reflectance rtaing of 49 to 62%.

SPECIFIC EXAMPLES OF THE INVENTION The following examples of the invention are given by way of illustration and not by way of limitation.

EXAMPLE 1 One hundred grams of poly(maleic anhydride) obtained by homopolymerization of maleic anhydride in the presence of maleyl-acetyl peroxide and boric acid as described in Blumbergs et al. patent application S.N. 862,059, filed Sept. 29, 1969 were dissolved in 400 ml. of distilled water at 60 to 70 C. and kept at this temperature for 2 hours. Sodium hydroxide solution was prepared in another beaker by dissolving 77 g. of NaOH pellets in 180 ml. of distilled water. Both solutions were simultaneously charged into a beaker, equipped with a laboratory stirrer and containing 100 ml. of distilled water, maintaining the pH in the range of 9.2 to 10.6. This was easily achieved by measuring the pH while regulating the flow rates of sodium hydroxide solution and poly(maleic acid) solution.

After all the solutions were charged into the beaker, 5 g. of 70% hydrogen peroxide were added and the stirring continued for an additional hour at 60 to 80 C. The slurry changed from pale yellow to white during this time. Then the slurry was evaporated and the solids were dried under reduced pressure. There were obtained 160 g. of white sodium polymaleate product.

The whiteness of this product was measured by the method of photoelectric tristimulus colorimetry, employing the Elrepho instrument, manufactured by Carl Zeiss in Germany. About 5 to g. of the product were made in a tablet, 45 mm. in diameter and 5 mm. thick, with the Elrepho powder press 45. After the tablet was made, it was placed on the measuring aperture and the reflectance value was read, using magnesium oxide tablet as the primary standard. The reflectance value of this sample was 94.2.

Run A (for comparison) The same as Example 1, only the mode of addition of the solutions was different. In this case, the poly(maleic acid) solution was charged into the caustic solution with good stirring. The pH of the mixture changed from 14 to 11 during the addition time. After all of the poly(maleic acid) solution was added, 5 g. of 70% hydrogen peroxide were added and the stirring continued for an additional hour. The color of the slurry changed from yellow to pale yellow. After evaporation under reduced pressure, 158 g. of cream-color solids were obtained. The whiteness of the product was 82.

Run B (for comparison) The same as Example 1, only the mode of addition of the solutions was changed. In this case, the caustic solution was charged into the poly(maleic acid) solution with good stirring while measuring the pH. After about a half of the caustic solution was consumed, the product precipitated out as large, gummy and sticky lumps. These lumps did not break down even by increased stirring speed. Up to this point, the pH showed a change from 2.3 to 7.0.

Also by adding additional sodium hydroxide solution, the lumps did not break down, but, on the contrary, increased in size. The product lumps were collected and analyzed and were found to be a mixture of sodium polymaleate and poly(maleic acid). No pure sodium polymaleate product was obtained by this procedure.

EXAMPLE 2 The same as Example 1, only the 5 g. of hydrogen peroxide were replaced with 10 g. of sodium hypochlorite solution having 5.5% of available chlorine. The whiteness of the product obtained was 92.8.

EXAMPLE 3 The same as Example 1, except that the 5 g. of hydrogen peroxide were replaced with 10 g. of 40% commercial peracetic acid. In this case, a small amount of sodium hydroxide solution was required to adjust the pH to 10.0. The whiteness of the product obtained was 93.9.

Run C (for comparison) The same as Example 1, only the addition of the hydrogen peroxide bleaching agent was omitted and the slurry was evaporated on a Rinco under reduced pressure without bleaching. The whitness of the product obtained was 56. The product was too dark to be used as a detergent builder.

Obviously, the examples can be multiplied indefinitely without departing from the spirit of the invention as defined in the claims.

Pursuant to the requirements of the patent statutes, the principle of this invention has been explained and exemplified in a manner so that it can be readily practiced by those skilled in the art, such exemplification including what is considered to represent the best embodiment of the invention. However, it should be clearly understood that, within the scope of the appended claims, the invention may be practiced by those skilled in the art, and having the benefit of this disclosure, otherwise than as specifically described and exemplified herein.

What is claimed is:

1. The method of making white finely divided sodium polymaleate which comprises (a) preparing an aqueous solution of poly(maleic acid) at a temperature not in excess of C.; (b) preparing an aqueous solution of a source of sodium oxide capable of reacting with the poly(maleic acid) to form sodium polymaleate; (c) feeding the two solutions into an aqueous liquor at a pH of 9.2 to 10.6 and maintaining the reaction mixture within that pH range and at a temperature not above 80 C.; (d) precipitating sodium polymaleate in said aqueous liquor to form a slurry; (e) bleaching the precipitated sodium polymaleate in said slurry while maintaining said pH range and (f) recovering bleached sodium polymaleate from the slurry.

2. The method of claim 1 in which the acid solution is near saturation at the temperature employed.

3. The method of claim 1 in which the temperature during acid solution and precipitation is kept between 60 and 80 C.

4. Process of claim 1 wherein said aqueous solution of poly(maleic acid) and the sodium oxide solutions are added continuously to said aqueous liquor, a portion of said slurry is continuously removed and bleached while maintaining its pH range of 9.2 to 10.6, and bleached sodium polymaleate is continuously recovered from its aqueous mother liquor.

5. Process of claim 1 wherein said aqueous liquor is a heel of water.

References Cited UNITED STATES PATENTS JOSEPH L. SCHOFER, Primary Examiner I. KIGHT, Assistant Examiner US. Cl. X.R. 252152 

